The present invention relates to network management, and, more particularly, to monitoring routing behaviour in a packet-switched network.
Packet-switched networks, such as networks based on the TCP/IP protocol suite, can be utilized by a network operator to provide a rich array of services. Networks of routers that store and forward Internet Protocol (IP) packets are becoming the single ubiquitous network for almost all communication needs. Within a single Autonomous System (AS) in an IP network, routing of packets is controlled by an interior gateway protocol, such as OSPF (Open Shortest Path Forwarding). See, e.g., J. Moy, “OSPF Version 2,” Request for Comments 2328, Internet Engineering Task Force (IETF), Network Working Group, April 1998, which is incorporated by reference herein. OSPF is a “link state” routing protocol, meaning that each router within the AS discovers and builds an entire view of the network topology. Every router running OSPF is responsible for describing a certain part of the network in a Link State Advertisements (LSA) which is flooded reliably to other routers in the network. The LSAs are utilized by each router to construct a weighted topological graph which the router uses to compute a shortest path tree. The router thereby builds a forwarding table that assures that packets are forwarded along the shortest paths in terms of link weights to their destination.
As users depend increasingly on a common packet-switched infrastructure for mission-critical needs, they require that the network provide increased reliability and support for new services. Systems for managing IP networks today, unfortunately, are targeted at element-level fault diagnosis and troubleshooting—and not to meet stringent needs of real-time resource tracking or provisioning for a given customer. For instance, to ensure reliability of the network it is important to ascertain customers who will be impacted by a particular interface failure. To provision capacity, e.g. for a given virtual leased line, it is critical to know the current topology of the network and thus know the path that the data for the line will follow. Current systems offer insufficient predictability in the network for a service provider to learn the paths that may be taken by some particular portion of the traffic coming into the network.